Preferential molecular encapsulation of an ICT fluorescence probe in the supramolecular cage of cucurbit[7]uril and β-cyclodextrin: an experimental and theoretical approach (original) (raw)
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Solubilization of Pyridone-Based Fluorescent Tag by Complexation in Cucurbit[7]uril
ACS Omega
Aimed at further exploring the hosting properties of cucurbit[7]uril (CB7), we have exploited the spectroscopic and photophysical properties of a known fluorescent label as the guest molecule, namely, 3-cyano-6-(2-thienyl)-4-trifluoromethyl pyridine (TFP), in neat solvents. The formation of an inclusion host−guest complex with CB7 was checked by UV−vis absorption spectroscopy, and the value of binding constant (9.7 × 10 5 M −1) was extracted from the spectrophotometric data. The modulation of keto−enol equilibrium in TFP by the local environment is governed by the interplay between dimerization through intermolecular hydrogen bonding between individual solute molecules, favoring the enol form, and intermolecular hydrogen bonding between TFP and the surrounding solvents, favoring the keto form. Time-resolved fluorescence results established that the macromolecular CB7 host stabilizes preferentially the neutral enol form over the keto form of TFP. Unprecedentedly, our results reveal a linear dependence of the amplitudes of the extracted decay-associated spectra from the time-resolved fluorescence spectra of TFP on the sum of polarity/polarizability and hydrogen bonding parameters of the local environment, confirming that TFP at micromolar concentration in the CB7 complexes is experiencing a methanol-like environment. The results rationalized the 42-fold enhancement in the solubility of TFP in water media by complexation in CB7.
In this paper, the binding interaction of a promising chloride channel blocker, 9-methyl anthroate (9-MA), with two different classes of molecular containers, β-cyclodextrins (β-CD and methyl-β-CD) and cucurbit[7]uril, having comparable cavity dimensions, has been thoroughly demonstrated via inspection of the modulation of the excited-state properties of the emissive molecule. Spectral data suggest that CB7 encapsulates the probe more efficiently in a 1:2 fashion, whereas the efficacies of β-CDs are relatively less and the corresponding stoichiometry is 1:1. Interestingly, despite being thermodynamically much more favorable than the probe−β-CD complexation equilibria, the fraction of probe−CB7 complex formed is appreciably smaller with respect to that of probe−β-CD complexes. This apparent inconsistency has been addressed via the proposition that since the formation of a 1:2 complex is entropically disadvantageous, it is anticipated that the activation barrier of the corresponding reaction is reasonably high, and thus only a small fraction of the reactants are able to surpass the energy barrier to form the products. This proposition has been thoroughly corroborated by fluorescence lifetime measurements at different temperatures.
Inclusion as a driving force for the intramolecular charge transfer (ICT) fluorescence of p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) in a-cyclodextrin (a-CD) aqueous solution Abstract A 1:1 inclusion complex between p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) molecule and a-cyclodextrin (a-CD) in aqueous solution is formed with a stabilization constant of ca. 45.65 ± 3.59 M-1 at 25 °C. The formation of the complex is accompanied by enhancement of the long wavelength fluorescence at 510 nm (attributed to intramolecular charge transfer (ICT) due to twisting) relative to the normal fluorescence at 420 nm. In water, the long-wavelength fluorescence is hidden under the red tail of the normal fluorescence band due to quenching by non-radiative transition. Inclusion by CD reduces quenching and thus constitutes a driving force for DPABME to emit at longer wavelength via ICT process. Keywords Guest–host inclusion Á Intramolecular charge transfer Á Fluorescence Á p-(N,N-diphenylamino)benzoic acid methyl ester (DPABME) Á Cyclodextrins
Molecular pharmaceutics, 2015
Host systems based on β-cyclodextrin (βCD) were employed as pharmaceutical carriers to encapsulate a poorly soluble drug, curcumin analogue (NC 2067), in order to increase its water solubility. βCD was chemically conjugated with an amphiphilic gemini surfactant with the ability to self-assemble and to form nanoscale supramolecular structures. The conjugated molecule, βCDgemini surfactant (βCDg), was shown to be a promising drug delivery agent. In this report, its physicochemical properties were assessed in aqueous solution using 1D and 2D (1)H NMR spectroscopy. The results showed that the apolar hydrocarbon domain of the gemini surfactant was self-included within the βCD internal cavity. The host/guest complexes composed of native βCD or βCDg with NC 2067 were examined using 1D/2D ROESY NMR methods. The stoichiometry of βCD/NC 2067 complex was estimated using Job's method via (1)H NMR spectroscopy. The binding geometry of NC 2067 within βCD was proposed using molecular docking a...
Journal of Molecular Structure, 2006
We present a detailed study on the binding of the naphthalene based fluorescence probe Prodan with two cyclic oligosachharides namely, natural beta-cyclodextrin (b-CD) and its synthetic derivative, succinyl-2-hydroxypropyl beta-cyclodextrin (SHPb-CD) using electronic absorption and fluorescence spectroscopy along with theoretical techniques. The encapsulation of Prodan inside the b-CD cavities leads to pronounced changes in its emission characteristics, including dramatic blue shifts (27 nm in 10 mM SHPb-CD and 19 nm in 10 mM b-CD) in the emission maximum accompanied by increase in the emission yield, fluorescence anisotropy and lifetime values. Detailed analyses of the fluorescence along with relevant absorption spectroscopic data indicate that Prodan readily enters the doughnut-shaped hydrophobic cavities of the b-CDs and forms 1:1 inclusion complexes, the binding affinity being significantly higher in case of SHPb-CD. Furthermore, docking studies performed via molecular mechanics methods (MMC) indicate that the dimethylamino group of Prodan is most likely to be oriented towards the wider rim of the cyclodextrin cavity. Quantum mechanical calculations reveal that incorporation of Prodan into the b-CD cavities, results in the formation of a N-TICT (dimethylamino twisted intramolecular charge transfer) state. q
Chemical Physics Letters, 2002
Spectral characteristics of 2-(4 0-N; N-dimethylaminophenyl)-1H-naphth[2,3-d] imidazole (DMAPNI) have been studied in aqueous b-cyclodextrin (b-CDx) solution. Enhancement in the fluorescence intensity of the normal band (B) is more than that of the twisted intramolecular charge transfer (TICT) band (A). pK a value for the protonation of @NA atom and the blue shifts observed in both the fluorescence bands suggest the encapsulation of DMAPNI in the hydrophobic cavity of b-CDx. Steady state and time resolved spectral analysis support the formation 1:2 complex between DMAPNI and b-CDx. Enhancement in the fluorescence intensity in aqueous b-CDx solution is due to the decrease in the non-radiative processes.